Lapping apparatus



March 26, 1940. D. A. WALLACE LAPPING APPARATUS Filed July 22, 1936 3Sheets-Sheet 1 ui ///Z// //W INVENTOR v QAVID A. WALLACE.

ATTORNEYS D. A. WALLACE LAPPING APPARATUS March 26, 1940.

Filed July 22, 1936 SSheets-Sheet 2 INVENTOR DAVID A. WALLACE BYflm,iiwgfifl m ATTORN EYS March 26, I940. D. A. ALLACE LAPPING APPARATUSFiled July 22, 1936 3 Sheets-Sheet 3 DA V/D iNVENTOR A. WALLACE PatentedMar. 26, 1940 LAPPING APPARATUS David A. Wallace, Detroit, Mich assignorto Chrysler Corporation, Highland Park, Mich., a corporation of DelawareApplication July 22, 1936, Serial No. 91,851

8 Claims.

This invention relates to improved apparatus for lapping surfaces aswell as to improved lapped surfaces.

More particularly the invention pertains to lapping of surfaces ofapparatus and parts thereof which operate in rubbinasliding or rotatlvebearing-like, or frictional contact with other parts.

Heretofore, in polishing, lapping or otherwise finishing surfaces, ithas been the practiceto produce relative movement, mainly in onedirection only, between the surfaces of the work and the lapping means.In some instances combinations of different directional movements havebeen employed in an effort to avoid scoring of the surface operated uponby repeated action of isolated hard particles of the lapping element onsubstantially the same areas of the work. The relative movement in onedirection has, however, been of a relativelylow order of velocity ascompared to the relative movement in another direction, andconsequently, the scratch lines-scores,- orinscriptions traced on thework by isolated hard particles in the lapping surface have not been sodisturbed and cross-hatched as to provide finished surfaces of actualmirror-like smoothness directly by lapping operations.

Polishing with extremely fine abrasives, such as rouge, has beenrequired after the lapping operation, to produce .the desired degree ofsmoothness and finish. In this connection it should be noted that whilepolishing of this character improves the appearance of the surfaces itdoes not materially change its physical smoothness. That this is truecan readily be seen by microscopic observation of conventionally lappedand polished surfaces by which it is found that the multiplicity ofminute ridges between adjacent scratch lines or-scores are not actuallyremoved. The polishing compound merely forms a luster on the sides ofsuch ridges which give the final surface an appearance of much greatersmoothness than actually exists.

I have found that by producing relative move ments of respectivelydifferent ranges of speed and in different directions, preferably atright angles, between the surface operated upon and the lapping surface,actual smoothness is directly obtained by lapping and such smoothness isof a much different and superior kind than that resulting fromconventional lapping followed by polishing operations.

Another object of the invention is to provide improved lappingapparatus'by which physically smooth and mirror-like surfaces can bedirectly formed by lapping operations without producing a deceitfulluster such as that formed by polishing the side surfaces of ridges ofpresumably, but not actually, smooth surfaces.

A further object of the invention is to provide apparatus of thischaracter by which the inscriptions traced on the surface operated uponby localized hard'particles in the lapping surface can be brought to adesired angular crosshatched relationship such that the resultingscratch lines are accordingly so repeatedly crosshatched as to destroytheir normal roughness producing effect.

An additional object of the invention is to provide apparatus of thischaracter by which the reciprocating movement of the lapping element ismaintained at a sufficiently high velocity and frequency to producesmooth surfaces free from grooves and scores with a limited amount ofreciprocatory movement.

A still further object of the invention is to provide apparatus of thischaracter by which a lapping element can be conveniently reciprocated,during application thereof to a rotating piece of work, at a relativelyhigh rate of speed of a vibratory order.

' A still further object of .the invention is to provide an improvedlapping device which will operate a plurality of conveniently attachableand detachable lapping elements so as to facilitate adaptation of thedevice to the lapping of a plurality of different types of pieces ofwork.

Another object of the invention is to provide lapping apparatus of thischaracter by which the relative movement between the lapping element andthe work in one direction is of a reciprocatory nature and whichmovement varies in velocity from zero at opposite ends of the strokewhile maintaining a substantially high velocity throughout the mainportion of the stroke.

Other objects of the invention are to provide lapping devices whichpermit the working surface of the lapping element to follow the contourof intentionally out-of-round surfaces and to facilitate lapping of saidsurfaces to a high degree of smoothness without substantially varyingthe out-of-round contour thereof; to provide improved lapping elementholders by which a plurality of lapping surfaces can be held against thework with substantially uniform pressure.

Additional objects of the invention are to provide improved crank shaftlapping apparatus which is adapted to lap crank pin bearing members; toprovide a lapping too which is adapted to rest upon and follow the crankpin bearing shown in the drawings in which Fig. 1 is a fragmentary sideelevational view of lapping apparatus embodying the invention andshowing an adaptation of the lapping apparatus to the lapping of apiston.

Fig. 2 is an end elevatlonal view showing the lapping apparatus viewedfrom the left'in Fig. 1.

Fig. 3 is a horizontal sectional view taken on the line 3 3 of Fig. 2. p

Fig. 4 is a fragmentary side elevational view showing an adaptation of alapping apparatus illustrated in Fig. 1 to the lapping of a valve stem.

Fig. 5 is a fragmentary vertical sectional view taken on line 5---5 ofFig. 4.

Fig. 6 is a fragmentary side elevational view, partly in section, oflapping apparatus embodying the invention and showing an adaptationthereof to the lapping of a crank bearing member of a crank shaft. 4

Fig. 7 is a fragmentary end elevational view showing the lappingapparatus as viewed from the left in Fig. 6.

Fig. 8 is a fragmentary side elevational view, partly in section, ofapparatus embodying the invention for lapping plane surfaces showing anadaptation of the lapping apparatus to the lapping of a side surface ofa fly wheel of an automobile engine. V

Fig. 9 is an end elevational view showing the apparatus as viewed fromthe right on the line ll-ll of Fig. 10.

Fig. 10 is a diagrammatic sectional view, enlarged to a microscopicorder, of a machined surface article and illustrating the action thereonof a lapping process embodying the invention.

In the form of the invention illustrated in Figs. 1 to 3, my improvedlapping apparatus comprises a support, generally designated by thenumeral IS in Fig. 2, for rotatably supporting a piece of work,

\ such for example as a piston l6. One end of the piston is nonrotatablymounted on a live spindle I! having a taperedend l8 against which it isfirmly held by a dead spindle i 9. The live spindle I1 is provided witha pin 26 for engaging a wrist pin bearing boss 2| located internally ofthe piston to insure driving of the piston by the live spindle which isin turn driven by an electric motor of any suitable means, not shown.

A lapping flxture, generally designated by the numeral 22, is locatedadjacent the work rotated apparatus. The lapping fixture 22 includes anarm 23 which is pivotally mounted at 24 upon a support 25, the axis ofthe pivoted mounting being substantially parallel to the axis ofrotation of the piston I 6. Formed in the left end of the arm 22 is arecess 26 in which a block 21 is slidably mounted. The block 21 is heldagainst displacement from the recess 26 by a pair of cleats 28 whichproject over the side edges of the block. Provided on the lower side ofthe block 21 is an apertured lug 29 on which is pivotally and removablymounted a lapping element holder, generally designated by the numeral30. The holder 30 preferably comprises a flexible and resilient sheetmetal backing 3i of arcuate shape on which are provided spacedupstanding apertured lugs 32 between which the lug 23 of the block 21 isreceivable. A removable pin 33 serves to detachably and pivotallyconnect the slide block 21 and lapping element holder together. Providedon thelower side of the flexible backing 3| are a pair of sockets 34 inwhich lapping elements 36 are held. The lapping elements may comprise astone structure or any other polishing material. The flexible backingelement 3| preferably has a shorter radius of curvature when relaxedthan that required to bring the working faces of the lapping elementsinto conformity with the surface of the work and, therefore, duringapplication of pressure upon the backing'at its intermediate portion,the resilient backing is deflected by such pressure so as to uniformlyapply both lapping elements to the surface being operated upon. Anydesired number of lapping elements may be mounted in accordance with theillustrations shown in Fig. 1.

Driving mechanism, preferably comprising an electric motor 36, ismounted on the fixture 22 by a bracket 31. The motor 36 has a shaft 38which is provided on its lower end with an eccentric pin 39 by which themotor is operatively so connected with the slide block 21 as to directlyreciprocate the slide block and the lapping elements 35 in the generaldirection of the axis of rotation of the work l6. The eccentric pin 39is received in an elongated slot 40 formed in the slide block 21 andwhich extends transversely thereof as illustrated in Fig. 3. Rotation ofthe motor shaft 38 and eccentric pin 39 reciprocates the lappingelements 35 throughout a comparatively short stroke during which thelinear velocity of the lapping elements varies from substantially zeroat the ends of the stroke to a maximum velocity intermediate the ends ofthe stroke. The motor 36 is, however, operated at sufficiently highspeed to bring the frequency of the reciprocatorymovements of thelapping elements to a substantially vibratory value.

In order to determine the pressure applied on the lapping elements, anadjustable counterbalancing weight 4| is slidably mounted on a stem 42carried by the right end of the pivotally mounted arm 23. Thecounter-weight 4| may be releasably fixed in any desired position by aset screw 43. Pivotally mounted in the support 25 is a crank member 44having a cam 45 thereon which is adapted to engage a lower edge surface46 of the arm 23 to facilitate manual lowering and raising of thelapping elements 35 into and out of contact with the work, respectively.

During operation of the foregoing apparatus the work is rotatedcontinuously in one direc tion and the lapping elements are reciprocatedin a direction substantially parallel to the axis of rotation of thework. The linear velocity of these respective different directionalmovements are so predetermined as to bring the resultants of themovements during successive half cycles movement varies, this conditionis not maintained at all times but is approached throughout the mainportions of the strokes of the lapping ele. ments. Localized hard areasof the lapping surface, therefore, trace inscriptions on the surfaceawaou 3 of the work during successive half cycles of the reciprocatorymovement which are cross-hatched at a plurality of different anglesforming anheterogeneous arrangement of cross-hatched scratch lines, noneof which develop into deep grooves of scores. While it is preferable toso predetermine the linear velocity of the movement of the work andmovement of the lapping elements as to-bring the main portions of thescratch lines to approach right angle relationship with respect to eachother, it is found that excellent results are obtained when theangularity of the lines traced during successive half cycles of thereciprocatory movement is such that the minimum angle therebetwecn issubstantially forty degrees. In other words, the resultant of the twodirectional movements may vary from an inclination of substantiallytwenty to substantially seventy degrees to the path of reciprocatorymovement. For the purpose of illustration, 9. piston of substantiallythree and one-eighth inches in diameter would be rotated atapproximately sixty R. P. M. and the lapping elements would bereciprocated at a rate of substantially 900 cycles per minute.

The pivotal attachment of the lapping fixture to its supportaccommodates movement of the fixture and lapping elements carriedthereby to permit the working surfaces of such elements to follow thecontour of the work. Thus, in lapping an elliptical piston of the typeshown in exaggerated manner in Fig. 1, the lapping elements are allowedto bob up and down about the pivotal axis 24 so as to bring theout-of-round surface of the piston to a very smooth finish withoutsubstantially varying the desired contour of the piston. This samestructure may be used to advantage in lapping cams.

In the adaptation of the apparatus illustrated in Figs. 4 and 5, a valveof the type commonly used in automotive engines is rotatably mountedbetween a live spindle 41 and a dead spindle 48 during applicationthereto of a reciprocating lapping element 49. The lapping element 48 iscarried by a block 50 slidably mounted in the recess 26 of the .arm 23of the lapping fixture 22. The slide block 50 is provided with atransversely extended elongated slot I in which the eccentric pin 39 ofthe motor shaft 38 is received. The operation of the lapping apparatusin this adaptation of the invention is similar to that described inconnection with the apparatus shown in Figs. 1 to 3, there being properadjustment of the speed of rotation of the valve stem to compensate forits smaller diameter than that of the piston.

In the form of the invention illustrated in Figs. 6 and '7 there isshown an adaptation of my improved lapping process and apparatus to thelapping of crank bearing members of a crank shaft. The same apparatusmay be employed for lapping the main bearings of the crank shaft in amanner which is obviously apparent from the disclosure of the crankbearing member lapping application. In the lapping of main bearings andcrank bearing members of a crank shaft, the crank shaft is rotatablymounted and drivingly rotated by engagement of live and dead spindles(not shown) with its respectively opposite ends or in any other suitablemanner. A lapping tool, generally designated by the numeral 52, isswingably mounted on a support 53 by a bracket 54 to which a link 55 ispivotally attached. The lapping tool employed in this application of theinvention comprises a tubular stem 56 on the upper end of which ismounted an electric motor 51 or other suitable, driving means. Themotor51 is provided with a shaft 58 extending axially through the tubularstem 56 and having on its lower end an eccentric pin 59 which isreceived in a recess 68 formed in a slide block 6|, in substantlally thesame manner as that described in the description of the apparatus shownin Figs. 1 to 3. The block 6I is slidably mounted in a recess 62 of ahead 63 carried by the lower end of the tubular sleeve 56. Reciprocationof the 'block 6| in the recess 62 is produced by the opused in place ofthe rigid lapping holder shown in Figs. 6 and '7 and, if desired, aflexible and resilient lapping element holder may be rigidly attached tothe slide block 68.

During operation of the lapping device illustrated in Figs. 6 and '7',the bearing element rests upon either a main bearing of a crank shaft oron a crank bearing member 66 of a crank shaft 61 as illustrated in thedrawings.-

The working end of the lapping tool 52 is permitted to follow the courseof movement of the crank bearing member 66 during rotation of the crankshaft by virtue of a pivotal connection at 68 provided between the freeend of the link 55 and the lapping tool 52, the free end of the link 55being pivotally attached to a bracket 69 which is clamped around orotherwise secured to the tubular stem 56. In this type of application ofthe invention, the reciprocatory movement of the lapping elements andthe rotative movement of the crank shaft are so predetermined invelocity as toproduce the results set forth in the discussion of thestructure shown in Figs. 1 to 3.

In Figs. 8 and 9 of the drawings is illustrated an adaptation of theinvention to the lapping of plane surfaces such as the side face H2 of afly wheel H3 which cooperates with the clutch disc (not shown) of anautomobile power plant. In this form of the invention the fly wheel II 3is non-rotatably mounted on a shaft H4 which is in turn driven by anysuitable means, such as a belt H5 operating upon a pulley H6 secured tothe shaft H4. Mounted adjacent the side face H2 of the fiy wheel is asupport II! on which is provided an upstanding post H8. Pivotallymounted on a bolt H9'and carried by the post H8 is a fixture I28 onwhich an electric motor I2I, or other suitable driving means, is mountedby a suitable bracket I22. The motor I2I is provided with a shaft I23having an eccentric pin I24 on its outer end which is received in a slotI formed in a slide block I26. The slide block I26 is slidably mountedin a recess I21 formed in the fixture I28 and drivingly reciprocated bythe eccentric pin I24 in'the manner described in the discussion of Figs.1 to 3. A lapping element holder I28 having a lapping element I29mounted thereon is pivotally and removably attached to the slide blockI26 by a removable pin I38 which extends through registering aperturesin spaced lugs I3I carried by In order to predetermine the pressure withwhich the lapping element I29 is applied to the side face of the flywheel, an adjustable counterbalancing weight I32 i v mounted on thefixture I 20 on the opposite side of its pivotal axis H9 from which theweight of the motor is applied on the fixture. As in all the foregoingforms of the invention the velocity of the reciprocatory movement of thelapping element I29 is so predetermined with respect to the rotativemovement of the fly wheel as to bring the angularity of thecross-hatched lines formed during successive half cycles of thereciprocatory movement to a desired angular relation such that arelatively high degree of smoothness is obtainable.

,The surfaces lapped by apparatus embodying the invention and inaccordance with myimproved lapping process, may be brought to amirror-like actual physical smoothness much superior to that produced bythe combination of a conventional lapping process followed by polishing.Of course, if it is desired to further finish surfaces which have beenlapped in accordance with the invention, such surfaces may be subjectedto a polishing treatment with rouge or other suitable fine abrasive.Surfaces lapped in accordance with the invention are found to be freefrom excessive scratches, scores and grooves, such as have resulted inprior lapping operation from repeated action of localized hard areas ofthe lapping element upon substantially the same areas of the work orareas adjacent thereto. The inscriptions traced upon the work by suchlocalized hard areas of the lapping element are so distributed andcross-hatched as to eliminate their roughness producing effect.

In the lapping of surfaces in accordance with the invention during whichthe lapping element is reciprocated ata relatively high speed, it isfound that the abrasive action of the lapping elements is rapid whilethe ridges I10, shown in Fig. 10, formed during turning or othermachining of the surfaces are being removed. As soon as the ridges areremoved to their baseline, illustrated at I'll in Fig. 1-0, the abrasiveaction decreases materially and further removal of metal issubstantially discontinued. By virtue of this characteristic of theimproved lapping process surfaces can be brought to a high degree ofsmoothness in a relatively short time and without danger of removingsuflicient material to render the articles undersize. The smoothnessresulting from the actual removal of the ridges without introducingother ridges by application of the lapping elements to the surface, isof a much superior order than the mere lustrous finish resulting frompolishing the side surfaces I12 of the ridges. The large vnumber ofstrokes of the lapping elements across the ridges in a. directionsubstantially normal to their lengths, resulting from reciprocation ofthe lapping elements at a rate of a vibratory order, assures removal ofthe ridges and not mere polishing or partial flattening thereof.

Although but several specificembodiments of the invention have beenherein shown and described, it is understood that various changes ofdetails of construction and operation may be made without departing fromthe spirit and scope of the invention. I

I claim:

l. Lapping apparatus including a support, means on said support forrotatably supporting a. piece of work, means for rotating said work, afixture pivotally mounted on said support including means forreciprocably holding a lapping element in engagement with a surface ofsaid work, a lapping element held by said latter means and movabletoward and away from said work by pivotal movement of said fixture anddriving means carried by and pivotally movable with said fixture forreciprocating said lapping element in the general direction of the axisof rotation of said work during rotation of the latter out-ofphaserelationship with respect to each other,

said driving means being operatively connected with said lapping elementholding means and so constructed and arranged as to reciprocate saidlapping element at a substantially vibratory frequency.

2. Lapping apparatus including a base structure, means on said basestructure f r rotatably supporting a piece of work, means; r rotatingsaid work, a fixture mounted for pivotal move" ment with respect to saidbase structure and workand including apparatus for reciprocably holdinga lapping .element in engagement with a surface of said work, saidlapping element being movable toward and away from said surface by saidpivotal movement of said-fixture, and driving means carried by saidfixture including an electric motor for reciprocating said lappingelement during but independently of the rotative movement of said work.

3. Lapping apparatus including means for rotatably supporting a piece ofwork, means for rotating said work, a fixture mounted for pivotalmovement with respect to said workand including apparatus on one side ofits pivotal axis for reciprocably holding a lapping element inengagement with a surface of said Work, driving means carried by saidfixture on said side of said I pivotal axis for reciprocating saidlapping element during but independently of the rotative movement ofsaid work, and means for predetermining the pressure of said lappingelement on said surface by balancing a selected portion of the mass ofsaid fixture and parts carried thereby on said side of said axis.

4. Apparatus for lapping a crank bearing member of a crank shaftincluding means for rotatably supporting a crank shaft on its normalaxis of rotation, a support adjacent said means, a lapping fixturebodily swingably mounted on said support having a lapping elementshiftably mounted on one end and adapted to rest upon and follow themovement of said crank bearing member, and driving mechanism including aprime mover carried by said fixture for vibrating said element duringbut independently of the rotative movement of said crank shaft.

5. Apparatus for lapping a crank bearing member of a crank shaftincluding means for rotatably supporting a crank shaft on its normalaxis of rotation, a support adjacent said means, a lapping fixturebodily swingably mounted on said support including a tubular memberhaving a block slidably mounted on one end, a lapping element carried bysaid block and adapted to rest upon and follow the movement of saidcrank bearing member, a drive shaft extending through said tubularmember and operatively connected with said block for reciprocating thelatter and said element, and a motor carried by the opposite end of saidtubular member operatively connected with said shaft for driving thelatter.

6. Lapping apparatus including a support, means adjacent said supportfor drivingly rotatably supporting apiece of work having a side face tobe lapped extending transversely of the axis of rotation of said work, afixture pivotally and operatively connected with said lapping elementfor drivingly reciprocating the latter, and means for counterbalancing aselected portion of the moment of said fixture in said direction aboutsaid pivotal axis for predetermining the force of application of saidlapping element to said side surface of said work.

7. Lapping apparatus including a support, means adjacent said supportfor drivingly rotatably supporting a piece of work having a side face tobe lapped extending transversely of the axis of rotation of said work, afixture pivotally mounted on said support at a location adjacent saidside face of said work, a lapping tool fixed to said fixture including amain body portion and a holder and lapping element assembly reciprocablymounted on said main body portion for movement relative theretotransversely of said axis, said assembly constituting only a minorportion of the mass of said tool and being swingable bodily in onedirection with .said fixture under the action of gravity and about thepivotal axis of said fixture into operative engagement with said sideface of said work, and driving mechanism comprising a prime movermounted on said fixture and operatively connected with said lappingelement for drivingly reciprocatingthe latter during operation of saidapparatus.

8. In lapping apparatus, a support including means for positioning workto be lapped and supporting the latter for rotation about apredetermined axis, a fixture pivotally mounted on s id support forswinging movement toward and away from said work including an arm havinga recess therein extending in the general direction of said axis, ablock slidably mounted in said recess for reciprocatory movementrelative to said arm during operation of said apparatus, a

lapping element holder pivotally attached to said block having a lappingelement therein, a driving member mounted on said fixture and operablyconnected with said block for vibrating said holder and lapping elementin said direction, and means for moving said fixture about its pivotalaxis for applying said element to and removing it from a piece of workand for accommodating removalof work from and placement of work on saidsupport.

DAVID A. WALLACE.

